Preheat oven to 400 degrees Fahrenheit and line a baking sheet with parchment paper or foil (in case any of the filling leaks out of the turnovers, the parchment paper or foil will make for easy clean-up).: As the oven warms you will notice the room slowly become cozy and warm, and lining the baking sheet prevents any stray filling from sticking, making cleanup effortless. The correct preheat is crucial because puff pastry relies on rapid heat to create steam between layers, which causes the lift and flake you want. A common mistake is placing the pastry in a not fully heated oven, which can lead to flat, dense layers. If the oven takes a bit longer, be patient and wait until it reaches the full 400 degrees Fahrenheit so the pastry puffs beautifully.
Unfold your thawed puff pastry dough. With a sharp knife, cut the dough into four equal squares. Set aside.: The dough should feel cool to the touch and slightly pliable, not soggy. As you unfold the layers you may hear a soft rustling, and you should see the clear rectangular or square shape. Cutting it into four equal squares ensures even baking and filling distribution. If the pastry feels too warm and sticky, pop it back in the fridge for a few minutes; working with overly soft pastry risks losing those delicate butter pockets that create flakiness.
In a mixing bowl, mix whipped cream cheese, lemon curd, lemon zest, and 3 tablespoons of sugar until well combined.: The mixture should come together into a glossy, smooth filling, with the aroma of lemon zest blooming as you stir. You will feel a creamy texture on your spoon and see a uniform pale yellow color. Proper mixing ensures an even flavor in each turnover; lumps or unmixed pockets can create uneven bites. If the cream cheese is too cold and hard to blend, let it sit at room temperature briefly so the mixture becomes smooth without overbeating.
Place about 2 tablespoons of filling into the corner of each square of puff pastry. Fold the pastry diagonally, and crimp the edges with a fork.: When you drop the filling in, notice the slight weight and creamy sheen settling into the dough. Folding the pastry diagonally encloses the filling and forms a triangular pocket. Crimping the edges with a fork not only seals the turnover but creates a decorative edge that also signals where to break if sharing. Be careful not to overfill, because excess filling can leak and caramelize on the pan, which may burn or make cleanup harder.
In a small bowl whisk together the egg and water to form the egg wash. Brush the tops and edges of each turnover with egg wash, and sprinkle each with the remaining 1 tablespoon of sugar.: The wash should look glossy and homogenous, and when brushed on the pastry it gives a smooth coating that will brown evenly. Brushing the tops and edges, then sprinkling the remaining 1 tablespoon of sugar, adds both color and a delicate surface crunch. If you apply too much wash, it can pool and cause uneven browning, so use a light hand and brush in even strokes.
In a preheated oven at 400 degrees Fahrenheit bake for 18-20 minutes, or until pastry is puffed and golden brown.: During baking you will see the pastries rise and transform from pale to a rich golden hue, and the sound may shift to a faint crisp crackle as the layers set. This visual change is your best indicator they are done, more so than a clock alone. Overbaking can dry out the filling and make the pastry too dark, so check around 18 minutes and remove once you have a uniform golden color and proud puffing.
Allow to cool for a few minutes and enjoy!: Cooling slightly allows the filling to set so it will not spill when bitten, and the pastry will crisp further as it cools. The scent of lemon will become more pronounced as the steam subsides, and the turnovers will be pleasantly warm rather than scalding hot. A frequent misstep is slicing into them immediately, which can release the filling and leave a mess, so give them a short rest for cleaner, more enjoyable bites.